Electric lamp



Oct. 17, 1939. A. RUTTENAUER ELECTRIC LAMP Filed Jan. 3, 193B LUMINESCENT COATING wumesceui' D COATING INVENTOR lfred Ruirienauer x 5.19mi,

A ORNEY Patented Oct. 11, 1

ELECTRIC LAMP Alfred Riittenauer, BerlinFHalensee, Germany,

assignor to General Electric Company, a corporation of New York Application January 3, 1938, Serial No. 183,206 In Germany January 15, 1937 2 Claims. (Cl. 176-122) The present invention relates to electric lamps of the gaseous discharge type and particularly to lamps producing at least part of their light by luminescence.

A particular object of the invention is to provide a lightsource of high luminous eificiency. Another object of the invention is to provide a source of light which will give a warm white light, similar to thatproduced by incandescent lamps. A further object of the invention is to provide a lamp of this type which will have a long useful life. Still other objects and advantages of the invention will appear from the following detailed specification or from an inspection of the accompanying drawing. I

The invention consists in the new and novel combination of elements hereinafter set forth and claimed.

Most gaseous discharges emit ultraviolet light in addition to the visible light. From time to time elforts have been made to convert these ultraviolet radiations into visible light, both to increase the luminous efliciency of the light source and to modify the color thereof. Since the mercury vapor discharge is especially rich in ultraviolet radiations and also has a high luminous efllciency of itself it is especially suitable for use in our novel lamp, but it is to be understood that the invention is not limited thereto.

In the copending application of McKeag and Randall, Serial No. 154,085, filed July 16, 1937, there is disclosed the use of zinc-beryllium silicate, wherein the beryllium and zinc are present in substantially equal molecular proportions, together with manganese as an activator, as a luminescent coating within a mercury vapor lamp to produce a white light. For general illumination a light that is warmer in tone than that provided' by the foregoing luminescent material is in some cases desirable. This requires additional red light. While this increase in the red can be obtained by an increase in the manganese to the range from 2-5%, this is undesirable, since the total light yield falls off rapidly as the manganese concentration is increased beyond the optimum range of from 0.5-1.5%. Hence some other means of increasing the red end of the spectrum produced by one of these lamps is much to be desired.

I have now found that this result is achieved by adding to the aforesaid zinc-beryllium silicate an equal amount of cadmium silicate (CdSiOs), which latter is preferably activated with 0.8% manganese. The cadmium silicate produces more luminescence in the red region than does the zinc-beryllium silicate, and I have also found that these two materialsmay be intermixed without either impairing the luminescent function of the other, the light yield for a given excitation with the mixed material being substantially equal to 6 ture now in common use, but other suitable gases are used where desired. The color of the light obtained is a warm white. The material is also used in hot cathode tubes for interior lighting.

Efficiencies between and lumens per watt are obtained; in lamps of the type specified known hitherto the efliciency has rarely, if ever, exceeded 30 lumens per watt.

I have also foundthat this novel luminescent material is particularly suitable for use in combination with high pressure mercury-vapor discharge devices, and more particularly with those in which the envelope is of quartz. The luminescent material is in this case applied, not to the interior of the envelope enclosing the discharge, but to some surface outside that envelope, for example, to the inner wall of a jacket in which the said envelope is normally enclosed.

For the purpose of illustrating my invention I have shown in the accompanying drawing two preferred embodiments thereof, in which Fig. 1 is an elevational view in part section of a low intensity lamp of the type used for signs, general illumination and the like, and

Fig. 2 is a similar view of a high pressure, high intensity type of mercury vapor arc lamp which is now well known.

As shown in this drawing, with particular reference to Fig. 1, my novel lamp has a sealed tubular envelope l of glass or the like with an electrode 2 sealed into each end thereof. As shown these electrodes are thermionic cathodes of the activated type which are heated to emission by the discharge, but it is to be understood that any other suitable type of electrode may be substituted therefor, and that where very low currents are employed, as in sign lamps and the like, that any of the well known cold cathodes may be employed. The envelope 1 containsany suitable atmosphere, but a filling of argon at a pressure of the order of 1.5 to 3.0 mm. plus sufilcient mercury to develop the desired pressure is preferred. A coating 3 of my novel mixture of zincberyllium silicate and cadmium silicate is produced on the inner surface of the envelope i in any suitable manner, many methods of producing such a coating being now well known.

When this device is energized to produce a discharge between the electrodes 3 the silicates are excited to luminescence by the ultraviolet radiations emitted by the discharge as well as by the direct impact of the discharge thereon, and the resulting luminescent light complements the visible light emitted by the discharge to produce a warm white light, similar to that produced by incandescent lamps.

In the device of Fig. 2 the discharge envelope 5 is of quartz or other ultraviolet transmitting material and has sealed therein a pair of electrodes 6 of the activated self-heating thermionic type. This envelope preferably contains a rare gas, such as argon, at a pressure of a few millimeters, plus a quantity of mercury which is usually designed to be wholly evaporated when the lamp reaches operatingtemperature, the pressure then being ordinarily of the order of an.

atmosphere or more. An enclosing jacket 1 01' glass or the like is provided about the envelope I to conserve the heat generated by the lamp.

This jacket is wholly evacuated, or when desired contains a gas such as nitrogen at a suitable pressure of say half an atmosphere. A coating 8 of my novel mixture of silicates, is provided on the inside of this jacket. Since the quartz en velope 5 is permeable to the ultraviolet radiations of from 2800 A. to 2000 A. and even less which excite this luminescent material the discharge within the envelope causes this coating to emit its characteristic luminescent light which complements the visible light from the discharge to produce a white light. Since the coating 8 offers but little obstruction to the visible radiations coming from the discharge the luminous efllciency of the unit is extremely high.

While I have disclosed my invention by reference to certain specific embodiments thereof it is to be understood that it is not limited thereto, but that various omissions, substitutions and changes, within the scope of the appended claims, may be made therein without departing from the spirit of the invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A lamp comprising an electric gaseous discharge device containing mercury and having a coating of luminescent material exposed to the radiations therefrom, said material comprising a mixture of substantially equal amounts of cadmium silicate activated with 0.8% manganese and zinc-beryllium silicate activated with 0.5 to 1.5% manganese in which the zinc and beryllium are present in equal molecular proportions, whereby the light produced by said lamp is a warm white having substantially the same high luminous efliciency as that of the zincberyllium silicate alone.

2. An envelope for an electric gaseous discharge device comprising a tubular vitreous body internally coated with a mixture of substantially equal amounts of cadmium silicate activated with 0.8% manganese and zinc-beryllium silicate activated with 0.5 to 1.5% manganese in which the zinc and beryllium are present in equal molecular proportions.

ALFRED RU'ITENAUER. 

